1. Field of the Invention
The present invention relates to a method for the synchronization of control functions with video signals in a television receiver as well as a device for the implementation of this method.
The television receiver has long been the instrument used to reproduce images received by an antenna and has been in instrument that can in no way be used to modify or create new images. This situation has begun to change with the appearance of integrated circuits and the creation of a data transmission system, namely the teletext system. Today, the television set is used not only to display teletext pages but also a menu. The menu is the element that enables an interactive control of the television set: the user's commands are sent to the television set by means of the remote control unit.
The commands or controls that prompt the display of the pages of text inform the user about the action resulting from his commands or guide him in his subsequent choices.
The new D2-MAC packet standard enables a novel application of these character generators: for, it provides the possibility of transmitting sub-titles in digital form and of controlling their display from the receiver. Thus, with his television set, the user now has at his disposal an image generator which, as the case may be, displays pages of teletext, sub-titles or a menu. It is clear that this list is not exhaustive and will become longer in the future.
In coming years, most television sets will include a character generator enabling a menu to be displayed on the television screen. The advantage of this approach is that it reduces the cost of the control function while the same time improving the reliability of the television set by reducing the number of push-buttons on the remote control unit.
2. Description of the Prior Art
The architecture of the television set corresponding to the usual case is shown in FIG. 1.
In the block diagram of this FIG. 1, the antenna 1 is connected to the intermediate frequency reception and amplification circuits 2. The demodulated output of the circuits 2 is connected to the input of a video cassette recorder 3 and to an input of a switch 4, the other input of which is connected to the output of the video cassette recorder 3. The output of the switch 4 is connected to two processing channels. The first of these channels has a chrominance decoder 5 and a RGB matrix 6. The second channel has a data separator 7 (namely data such as teletext data) and a character generator 8 with which there is associated a memory 8A. The character generator 8 is controlled by a microcontroller 9 that works in cooperation with a remote control box 10 (generally infrared). The RGB outputs of the circuits 6 and 8 are each connected to an input of a switch 11 that is followed by a video amplifier 12 and the cathode-ray tube 13. The switch 11 is controlled by the generator 8.
It can be seen that, in a system such as this, the video cassette recorder never records the output of the character generator. It is clear that this architecture cannot be used when a D2-MAC packet decoder is used: in fact it is indispensable, in this case, to record the sub-titles when they exist.
In the block diagram of FIG. 2, the same elements as those of FIG. 1 are assigned the same numerical references. The antenna 1 of the television set of FIG. 2 is connected, firstly, to a first intermediate output frequency tuner 2A that relates to the amplitude modulated channel and has a reduced sideband.
The antenna 1 is furthermore connected to a second intermediate frequency tuner 2B, relating to the frequency D2-MAC modulation channel.
The output of the tuner 2A is connected to a first input of a switch 4A with three inputs and to the input of the video cassette recorder 3, the output of which is connected to a second input of the switch 4A. The third input of the switch is connected to the CVBS (Composite Video Baseband Signal) output of the tuner 2B. The switch 4A is followed, firstly, by the circuits 5, 6, 11 and 12, and, secondly, by the circuits 7 and 8. A switch 14 is interposed between the circuits 8 and 11. The generator 8 is controlled by the microcontroller 9 cooperating with the remote control unit 10.
Downline from the D2-MAC output of the tuner 2B, there are respectively connected a MAC decoder 15, a data separator 16, a character generator 17 and a switch 18, one input of which is connected to the decoder 15, this switch 18 being controlled by the generator 17 with which a memory 17a is associated. The output of the switch 18 is connected to an input of the switch 14 and a PAL coder 19, the output of which is connected to the video cassette recorder 3'. An output of the generator 8 is connected to a free input of an OR gate, the other input of which receives the D2-MAC signals from the tuner 2B. These D2-MAC signals also control the switch 14.
Thus, in the device of FIG. 2, it can be seen that the D2-MAC decoder 15 and the associated character generator 17 are designed as an independent sub-assembly. In this case, the television set has two character generators 8 and 17, and notably one character generator used only for the sub-titles (17). The video cassette recorder connected to the PAL encoder therefore records only the sub-titles and not the menu (which is produced by the character generator 8). The major drawback of the approach is its cost: for, it is necessary to use two character generators.
A more economical approach used INTERMETALL brand digital integrated circuits. Its architecture has been designed so that the D2-MAC circuit and the character generator generate the basic elements of a complete device.
FIG. 3 shows the new circuits of this approach. The other circuits (not shown) are those connected upline (intermediate frequency tuner in particular) giving the D2-MAC and CVBS signals, and those connected downline (video circuits receiving the RGB video signal).
This device of FIG. 3 includes an analog/digital converter 21, the output bus 22 of which is connected to: a scanning processor 23 for the cathode-ray tube of the television set, a video processor 24, a MAC decoder 25 and a CVBS data separator 26. The output bus of the circuits 24 and 25 are connected to a digital/analog converter 27. The decoder 25 is connected to a MAC data separator 27. The decoder 25 is connected to a data separator MAC 28, which is itself connected to a data generator 29. This generator 29 is also connected to the CVBS separator 26. The output of the generator 29 is connected to the converter 27. The RGB analog output of the converter 27 is, firstly, connected to the video circuits (not shown) of the television set and, secondly, to an encoder 30 which is a PAL encoder herein. The output of the encoder 30 is connected to the video cassette recorder 31.
It is therefore possible, in this circuit of FIG. 3, to use only one character generator. However, it is then no longer possible to distinguish the characters corresponding to the sub-title from those corresponding to a menu, and it is doubtful whether the user would wish to record the menu on his video cassette recorder.